Differential superior prefrontal activity on initial versus subsequent shifts in naive subjects.

Flexible adaptation to changing environments requires shifting of a cognitive set, one basic function of the prefrontal cortex. Set shifting, as instantiated in the Wisconsin Card Sorting Task (WCST) administered in a neuropsychological testing room, is typically achieved when subjects have no prior experiences of updating one WCST behavior to another. By contrast, earlier neuroimaging studies typically involved examination of repeated transitions between particular behaviors, to which situation subjects are far from naive. Naive subjects with no prior knowledge of the WCST were recruited in the present functional magnetic resonance imaging study to test set shifting under unknown situations that they experienced for the first time. Prominent activation was revealed in the left superior prefrontal cortex selectively on the initial shifts. On the other hand, the inferior prefrontal cortex was significantly activated on both the initial and subsequent shifts. The superior prefrontal activation distinguishable from the conventional inferior prefrontal activation suggests a selective role of this region in performance of the WCST in naive subjects.